Drywall as an exterior finished siding alternative?
This may be coming out of left field, but what are your thoughts on using drywall as an exterior siding? No stucco, no fiber cement, no engineered wood, no vinyl — just install exterior rated drywall like Densglass, taped with exterior rated joint compound and maybe Fibafuse, then painted with a few coats of a good paint.
This would be installed over a rainscreen made up of 3/4″ thick furring strips 24″ O.C.
I got to thinking about this because drywall (regular, not even exterior rated) is the most common material to use for patio ceilings around here (Phoenix, AZ). What, I thought, if I also used it on the walls, just with better drywall?
Why not go with stucco? Well, it’s nigh impossible to find a contractor around here to deal with small projects and even though I’m building 99% of the house myself, I do know my limitations and stucco feels like something just past my skill level.
Why not standard siding like James Hardie or LP SmartSide or the like? They are inexpensive and easy to install, yes, but I just don’t like the look of them and would only go that route if the “smooth wall” route can’t pan out.
I wouldn’t be too concerned with water since most of the house is surrounded by 10′ patios and the parts that aren’t have 2.5′ eaves. Only the bottom of the walls will even get wet at all and that’s mostly from blown rain or bounce-back. With how little rain Phoenix gets plus my rainscreen, I can’t imagine the walls would stay wet for long. And it’s exterior rated drywall anyway.
Incidental damage could be a concern since the drywall wouldn’t be a strong as most of the other options, so a kicked-up rock or something could definitely dent or puncture it. In a weird way, I wonder if it would be better than many of the alternatives, though, if only because of how easy it is to repair drywall vs something like stucco or conventional siding.
What am I missing?
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No, nope, not a chance. Here in the humid northeast I've been involved with a couple of house projects that had drywall ceilings on porches or overhangs and even those ultimately failed and were replaced with mold-resistant materials. Even in a dry climate I would never use a moisture-sensitive material for such an important part of my house, or a client's.
The drywall in the porch ceiling is ubiquitous here in Phoenix - I have never seen a patio that didn't use it. I've never heard of a problem with them in that context because they will never get wet from rain and the humidity is typically extremely low around here -- the max average humidity is 51% in December and most months it is less than 40%.
But I still wouldn't trust normal drywall on an exterior wall. That's why I was thinking of something like Densglass, which is rated by the manufacturer for full weather exposure for 12 months under warranty. So likely not fully waterproof, but certainly as water resistant as most typical exterior coverings.
kurtgranroth,
Being the first-adopter always comes with risks. It might work, but it would be a pretty expensive lesson to find out if it didn't.
As a general rule of thumb, if something that cheap and simple worked, spec builders would be all over it. You probably haven't seen it for a reason.
Yes, this is precisely why I was asking! If spec and high-output builders in places like Texas are okay using essentially cardboard as the exterior sheathing material instead of plywood or OSB, then why wouldn't they also do something like my proposal instead of stucco if it was an option?
Now, I have seen several references to using Densglass as the substrate under plaster ("render" in the UK) and that feels like just a step or so beyond what I was thinking.
One thought I had was that maybe environmental conditions could cause the exterior to move more than the interior and could it cause more cracks? It DOESN'T cause the regular drywall on the patio ceilings to crack so maybe not.
I would LOVE to hear from somebody who tried this or knows somebody who did. Maybe not finding such a person should give me the answer I'm looking for, though!
I would also caution against your plan. If it is truly protected from nearly all water, it might actually work, but I can't imagine it looking any good over time. Also, if you have any reasonably diligent code enforcement, they wouldn't let you do this. Dens Glass is rated for use as a sheathing, not a finish material, and manufacturer's standards are generally followed as Code for most projects.
There is an alternate system that you might consider, though: DEFS (Direct-applied Finish System). This is not an appropriate treatment for wet climates, but it might work fine for yours. It is approved by the appropriate test labs as an exterior cladding. It consists of cement board (Durock, etc) as the substrate. Seams are taped and mudded with acrylic modified cement plaster, and then the whole sheet is covered with a thin coat of the same stuff. This is applied by trowel, so there is some skill involved, but nearly so much as with traditional cement stucco. It also goes on just thick enough to cover the texture of the cement board and the taped seams. Once everything is smooth and dry, the sanded acrylic finish is applied. Again, this is trowel work but not all that difficult to learn the skills. The final look is identical to either stucco or EIFS with a smooth sanded finish, but the system is somewhat cheaper and faster to install. It is possible the Dens Glass is approved as a subtrate for this system, but I am not familiar with any manufacturers who have specified the system that way. This may have changed recently though. If you Google DEFS, you'll find your way to the major manufacturers of these systems.
Thanks. I honestly hadn't thought of the "code enforcement" aspect but yeah, that's the deal breaker right there. I have a strong suspicion (based on my interactions with the local inspectors to date) that they wouldn't care at all but the risk if I was wrong is far too great and so my idea is a non-starter.
Thanks for the DEFS reference -- I hadn't heard of that before and a variation of that might actually work for me. The key is that I'm going to be doing it completely alone and I work excruciatingly slow and any process that requires maintaining a "wet edge" (like classic stucco or plaster) isn't going to work. But if it is just taping seams (a week) and then can skim coat one panel at a time (day, each), then that fits my pace.
From a gba article
“Another new product comes from Georgia-Pacific, maker of DensShield. Their DensDefy Liquid Barrier is a single-component, liquid-applied WRB. Once applied, the fluid film sets to a seamless, durable membrane on exterior gypsum sheathing, wood sheathing, CMU, and concrete walls. It’s spread with a roller or spray in temperatures as low as 25ºF and it cures in temperatures as low as 32ºF. The company sells a suite of compatible liquid flashings and transition membranes to bridge gaps between dissimilar materials.”
https://www.greenbuildingadvisor.com/article/materials-for-high-performance-building-envelopes
Does this help bring us closer to installing a gypsum siding product in cz7?!?
Around me gypsum sheathing is about the same cost (or close enough) to Hardie panel, I can't see why you would not use that instead. You can put battens over the seams (what I did on my home) or go for Z trim for a more modern look.
Gypsum sheathing is great for what it is meant for. It does take a lot of abuse but I would not trust it exposed.
Haha, I now have Michael, Malcom, Peter, Bill, and you all telling me that the drywall option is a terrible idea so yeah, I would have to be a fool to continue on the clearly treacherous path!
I do really like the Hardie panels since the panel look with z-trim is right up my modern-loving wheelhouse. Alas, my wife has vetoed any look that isn't either completely smooth (ala plaster/stucco) or lap siding.
Densglass is commonly used on commercial building exteriors, but there is always some kind of cladding over it. I've never seen densglass left exposed. If you were to try something like this, I would at least use a high-end fluid applied WRB over the taped densglass assembly to act as a sort of exterior cladding, then paint over that. You'd end up being a sort of experimental construction project though, so it's difficult to say how well things would hold up over time. I would be particularly careful with flashing details around all edges of the densglass "siding" if you were to try this.
Bill